‘It is an attack on the balance of the constitution and therefore is is unlawful.’

David Johnston QC, representing the UK Government, had argued it was not for the courts to get involved in what was a political decision.

The campaigners who joined SNP MP Joanna Cherry included Liberal Democrat leader Jo Swinson, Labour MP Ian Murray and anti-Brexit barrister Jo Maugham, of the Good Law Project.

New Lib Dem MP Luciana Berger tweeted: ‘As one of the petitioners to this case, this is such an important ruling – although how awful that it’s had to come to this. ‘

SNP Westminiter leader Ian Blackford tweeted Ms Cherry, saying: ‘This is great news, congratulations to you and all involved. This battle has further to run but my message to @BorisJohnson is you are playing fast and loose with the law.

New Lib Dem MP Luciana Berger (second right) was one of the petitioners (Picture: PA)

‘You have acted in an anti democratic manner and need to respond by recalling Parliament.’

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Lawyer Jo Maugham said an appeal to the Supreme Court, the highest judicial body in the United Kingdom, would begin next week.

He tweeted: ‘We have won. Appeal begins in the Supreme Court on Tuesday.

‘We believe that the effect of the decision is that Parliament is no longer prorogued.

‘I have never been able to contemplate the possibility that the law could be that our sovereign Parliament might be treated as an inconvenience by the Prime Minister.

We believe that the effect of the decision is that Parliament is no longer prorogued.